Window and the like



PatentedjApr. 21,1942

William Hen r-y Moss, London, England, asaignor to Celanese Corporation of America, a corpora-v tion of Delaware some. Application January 31, 1939,85 iigliNo. 253,811. In Great Britain February 8, i

I 12 Claims. (cm-i4) This invention relates to windows andthe like and especially to respirator eye-pieces and other be dissolved inaqueous acetone, preferably together with, a small proportion of ethyl lactate,

transparent closures which are required to remain transparent under conditions'in whichthey would normally become obscured by the condenwhen of moisture upon them, and tocomposite sheet material adapted to form such closures.

sheet material. n l

Bespirator 'eye-piecesare subjected in use to a moist, warm atmosphere on theinner side and The invention includes 'the production of such to a colderatmosphere onthe outer side. In

consequence they tend to become obscured by the condensation ofmoisture on theinside." In U. S. application S. No. 225,5'l0filed August 18, 1938,

I havefwindicated how, this disadvantage can be overcome by forming at least thatsurface of the eye-piece which is liable to become fogged, of a cellulose acetate which hasb'een made byhydrolysing aprimary celluloseacetate considerably beyond theince'ption of acetone-solubility until it becomes soluble in acetone diluted to a considerable extent with water while still insoluble in, and not unduly swollen by,liquid water. Such a cellulose acetate is found to be capable of absorbing-water vapour. This prop erty togetherwith theproperty of belnginsoluble in, and not unduly swollen by, liquid water are to be regarded asconnoted by the term hydrotropic as used herein. The invention is; not concerned with small differences in water resistance such as areof no commercial utility. Thus for a sheet materialto be regarded ashydrotropic'f it should at least be capable of being held close to the mouth and breathed upon several times without dimming where a water-resistant" material should under the same conditions become fogged. The degree oi resistance to swelling called for in the hydrotroplc material is suiiicient merely to prevent buckling of the composite sheet material under the conditions of use. i

The composite sheet material of the: invention 7 comprises a basic sheet of aawater-resistant cel- V lulose acetate or other film-forming polymeric ester of ether and adherent thereto. an outer sheet of a cellulose acetate, or other film-forming polymeric ester or ether, which is hydrotropic.

The hydrotropie cellulose acetate for surfacing the eye-pieceor thelike maybe made, for example, by treatinga primary cellulose acetate solution in acetic acid made by the usual acetylposite sheet is required. Thicker sheets can be diacetone alcohol or other highor medium boiling solvent. From this solution a sheet or foil may beformed which maybe caused to adhere to a sheet of ordinary cellulose acetate of the desired dimensionsby the application of pressure in the presence of a suitable solvent for either the hydrotropic or the water-resistant material, for ex-, V

ample in the case of cellulose acetate acetone.

The adhesion may be efiected by the combined actionoi heat and pressure using, e. g. instead of a true solvent a liquid which becomes a solvent at elevated temperatures, e. g. 80% aqueous ethanol or methanol in the case of'cellulose acetate. Or

assisting liquids may bedispensed with but it is then more diflicult to secure good adhesion. In-' stead of forming a sheet orioil of the hydrotropic celluloseacetate, on a separate film-forming surface the sheet or foil may be formedon the basic sheet, e. g. by spraying or casting methods. This method is to be preferred when J the outer sheet is to be of small thicknesse. g.

of the order of 0.01" orless. The basic sheet maybe surfaced on one orboth sides with the hydrotropic cellulose acetate. With a view to assisting the eye-piece to retain its shape and flatness in spite of varying conditions of moisture it is of advantage tosuriace both sides.

The basic sheet can be made by flowing, or extruding a composition containing the waterresistant cellulose acetate and a plasticiser dissolved in a volatile solvent on tola travelling filmforming surface, for example the surface of an endlessdrlven metal band, and effecting evaporation of the volatile solventduringthe travel of the bandor otherwsurface. The foil or sheet of hydrotropic celluloseacetate for surfacing the basicsheet may be formed in a similar way. This. method is most suitable when a thin comcut from a block made by compressing a moulding powder containing the cellulose acetate and plasticlsers and the like in a heated block press. An

alternative method of forming the basic sheet is,

to build it up by spraying on to a suitable sur- Y iace a solution of the cellulose acetate, which may ation process using sulphuric :acid 'as the acetyl ation catalyst, for a prolonged period with water until it attains solubility me 50% aqueous solution of acetone. The cellulose acetate may then with advantage contain, in addition to the volatile solvent; and the plasticiser for the cellulose acetate, one or more high boiling solvents tor the cellulose acetate, for example'diacetone alcohol or ethyl lactate, and one or more medium boiling non-solvents, for example methanol or ethanol. In a similar way the outersheet can be formed; or, as indicated above, this may beiormed in situ by spraying on to the basic sheet a solution of the hydrotropic material in a volatile solvent therefor.

A convenient thickness for the surfaced sheet from which eye-pieces or the like can be cut is between 0.005" and 0.015, for example 0.007"

,to 0.011". Thus, for example, .the basic layer may conveniently have a thickness of 0.004" to 0.006" and may be surfaced on both sides with a foil or coating of hydrotropic cellulose acetate of thickness from 0.001" to 0.002" or 0.003";,o ra somewhat thicker foil, sheet or coating of hydrotropic cellulose acetate, for example of thickness comprising two relatively thick surfacing layers .both layers and particularly in the outer.

amplesof such modifiers are high boiling alcoof hydrotropic celluloseacetate reinforced with a thinner layer of watereresistant cellulose ace:

The water-resistant cellulose acetate for forming .the basic or reinforcing sheet should preferablyhave been made by acetylation under such conditions that degradation. of the, cellulose molecule is .substantially avoided, followed by.

ripening to acetoneesolubility, forexample to an acetyl value of 51 or 52 to 53 or 54%calculated as acetic. acid. With a viewto avoiding substanin. the final product. Halides of. amphoteric metals, for example-ferric chloride or zinc chloride, can be used as acetylation catalysts in place of sulphuric acid. ,The acetylationproduct may be ripened in solution or in suspension- 7 in an inert liquid, for example benzene, to an" acetyl number within the limits mentioned above. The hydrotropic cellulose acetate forming the basis of the surface. layer or layers, can, as indicated above, be made in asimilar way to. that for use in the basic layer except that ripening is continued considerably beyond the inception of acetone-solubility. until, for instance, the cellu-' lose acetate is soluble in aqueous acetone 1 or even in acetonecontaining a larger per cent of water, for example -75 or -An alternative-or additional expedient which may .be

adopted to obtain similar properties in the cellulose acetate for the surfacing layer is acetylation under such conditions that partial breaking down of the cellulose molecule occurs, for ex-: ample the use of higher proportions of catalyst; higher temperatures and a lower proportion of diluent. A further expedient is to subject the cellulose from which thecellulose acetate is tobe made to a preliminary treatment, for example having a greater affinity for water, for example dimethyl-, diethyland dibutyl-tartrates, dioxyethyl phthalate, ethyl acetanilide and sulphonamides and sulphonanilides, for example paratoluene sulphonamide, Among plasticizers particularly suitable for the basic layer are ethere'sters such as. diethoxyethyl phthalate and dimethoxyethyl phthalate. Other modifying agents (i. e. agents adapted to modify the mechanical properties of the sheet material) having an afilnity for water may, with advantage, be present in hols, e. g; glycol, glycerol and diacetone alcohol and synthetic resins having an aflinity for water, e. g. those obtainable (as described in British Patent No. 453,833 corresponding to U. S. Patent No. 2,153,585 by condensing an alcohol containing at least two hydroxy groups with hydroxy polycarboxylic acids, with formals of such acids or with fatty acid esters of such acids. Specially suitable are the condensation products of glycerol with citric acidand with methylene citric acid. Synthetic resins having little or no affinity for water, e, g, the condensation products of formaldehyde with polynuclear phenols such as diphenylol propane and with sulphonamides, e. g. para-toluene sulphonamide may also be present particularly in the basic layer.

The invention has beendescribed above with particular reference to the use of cellulose acetate as the basis for the basic and outer sheets, This is not, however, essential. .Thus, for example, the basic sheet may comprise cellulose nitrate, cellulose propionate, cellulose butyrate, cellulose acetate-propionate, -cellulose acetate-butyrate, cellulose acetate-nitrate, cellulose propionatenitrate, cellulose butyrate-nitrate, oxyethyl cellulose acetate, ethyl cellulose acetate, ethyl cellulose, benzyl cellulose or other water-resistant transparent film-forming substances, for example polymerized unsaturated compounds such aspolyvinyl acetate, chloracetate ,or chloride, polymerised acrylic esters or alkyl substituted esters. Similarly, the outer sheet or sheets may be formed from any of the organic or mixed inorganic-organic esters referred to above, ripened or saponified to a point at which they have a reduced water-resistance without becoming waterwith mineral acids, formic acid .or mixtures thereof with acetic or other lower fatty 'acids, with a view to effecting some breaking down of the cellulose molecule before acetylation, I

Plasticizers may be present in the'outer as well as in the basic sheets. Plasticizers for the outer layer should preferably have at least some slight degree of affinity for water. Thus, highly water-' resistant plasticizers such, for example; as tricresyl phosphate, tributyl phosphate and dibutyl phthalate, if employed at all in this layer, should preferably be in admixture with plasticizers soluble or capable of swelling to an undue ex tent in water.'. Substances similar to those referred to above but having a reduced water-resistance owing, for example, to partial breaking down of long molecular chains in their manufacture may be used in forming the superficial layer. 1 It is of advantage for the ester or ether of the outerand basic layers to be formed. from the same ester-forming or ether-forming components for said ester or ether or at least to be so similar in constitution as to have an. afllnity for one another. Thisfacilitates union of the sheets and simplifies the choice of suitable plasticizers.

Althoughthe process and products of the invention are .of particular importance in connection with the manufacture of respirator eyepieces, goggles and the like they have other applications, for example in the production of wind-screens or windows for closed vehicles, aircraft, gun turrets and the like, The products of the invention are capable of remaining undimmed for considerable periods even when exposed on one side to a saturated atmosphere at blood heat and on the other to a winter atmospheric temperature. The invention includes following composition Inadej made by the methodstdescribed above, e. g. respirator face-pieces and goggles having such eye-pieces. w e e The followingexamples illustrate the invention:, I

p Eramplefi l A hydrotropic cellulose acetate is made as follows 100 parts of 2,280,097 articles provided avith eye-pieces or windows e e acetatejhas the following composition:

hours area-'40 c. with 100 parts of acetic acid.

, The mass isthen added to amixture, precooled to about C., of 300 parts of acetic acid, 300

parts of acetic anhydrideand parts of sulphuric acid. Acetylation is allowed to continue until all the cellulosehasdissolved, the temperat ture not being allowed to rise above'j about C.

lcellulose arefprtreated forl2 and the solution or hydrotropic cellulose a P'arts Cellulose acetate having its maximum solubility in 40% aqueous acetone, 20 Methylene citric acid glycerol resin 10 lDioxane 5 Water V The cellulose acetate is made as described in *Example 1 ripening being continued until the specified solubility is. obtained. The methylene citric acid glycerol resin is made by heating 20.4 parts ofmethylenefcitric acid with 6 parts or glycerolin an open vessel at 180 C; until the test" sample gels when heated for 10 minutesat v 185-190 C. in a'closed' tube in an oilbath as described in British Patent-No."453,833 corre- 40-50 parts of water are then added and ripening is effected by allowing the mixture tostan'd at a temperature of -130" C.; untilj a samplefre moved is. soluble in a %aqr1eous solution of, acetene. Prematureprecipitation during ripen ing is avoided by the addition of further quantities of water fromtime. to time. The cellulose acetate is then precipitated bythe addition of aceteneQfiltered, washedinacetene and dried.

From this cellulose acetate a solutionofthe e e Parts Celluloseacetatem n l0 Glycerol; j 1 Diethylene glycol Dioxane 20 T "T In this aslin all the examples, all the partsiare by weight. A i i a:

The solution is flowed on to a sheet'of thickness .04 and of the following composition:

I a e l Parts Acetone-soluble cellulose acetate 80-55 finished sheet, respirator eye-pieces can be cut.

spohding to'U, S, PatentNo; 2,153,585! Instead of using methylene citric acid and glycerol, condensation may be efl'ected in'asimilar way be-. tween citric acid glycerol and paraformaldehyde.

. Instead of flowing thelsolution directly on to thebasic sheet it may asin Example 2; beilowed on to a suitable film-forming surface andthe resulting sheet may then be stripped therefrom and uiiited with'the basic sheet under heat and pressure with the help of a suitable adhesive,

for instance a solution of' polyvinyl acetate in methanol or ethanoll The solution offhydrotropic cellulose acetate 7 may be replaced by either of the solutions of Examples' 'l and 8 of U. S. applicationfSerial No.

225,5'7Qnled August 18, 19 38,

' Example 4- e A sheet of. thickness 0.015" and of the composition of the basic .sheet in. Example 3 is sprayed on both sides with a solution of the following composition: e

. e Parts Hydrotropic cellulose acetate 20 Methylene citric acid glycerol resin 10 Waterj- 100 Dioxane 4---; 100

The solution of hydrotrop ic celluloseacetate The hydrotropic cellulose acetate is made as in Example 1. The composite sheet material is finishedas described in Example 1. a g

In all the foregoingexamples the hydrotropic cellulose acetate may be made by other methods than that described in Example 1, for example by the methods described in Examples 11 and 12 of U. S. application Serial No. 225,570 filed August ample 1. This sheetis thenwettjedwithian alcoliolic solution ofpolyvinylacetate of. medium viscositykk A basicgsheet of the thickness and.

composition of that in Example I is wetted with the same solution and the two sheets are then brought together with their wetted surfaces in contact. The assembly; is pressed in a heated platten "press to secureadhesion. During the pressing thealcoholisvaporised. The composite sheet obtained issuitable for the construction of observation panels of aircraft or windows of closed motors vehicles.

material inside. i l

' Example 3 The process is carried out as in Examplei ex cept than 4-8 parts of the dimethyl phthaiate are replacedby methylene citric acid glycerol The sheet materials of the invention may be shaped in any desired .way. Thus, for example, curved observation panels for aircraft may be formedby cutting the sheet material to the it necessary size and bending the material in a suitable cement, lacquer or the like but this is In such use the sheet I material is fixed with the surf-ace of hydrotropic 7 'in general unnecessary.

Having described myinvention what I "desire to secure by Letters Patent is: e y e 1. A transparent window closure for an article in the use of which said-closure will be exposed that is an ester of an organic acid, and adherent thereto at least one outer layer of a hydrotropic water.

film-forming polymer that is an ester of the same organic acid and the same alcohol as the water- I resistant polymer.

' 2. A transparent window closure for an article in the use of which said closure will be exposed to conditions of temperature and humidity tendto cause fogging by the condensation of moisture thereon, said closure comprising a layer of a water-resistant organic film-forming, polymer resistant polymer, said hydrotropic'polymer being soluble in an aqueous solution of a suitable organic liquid containing at least 50% of water, but insoluble in water. "3. -A transparent window closure for an article in the useof which said closure will be exposed to conditions of temperature and humidity tending to. cause fogging by the condensation of moisture thereon, said closure comprising a layer a water-resistant organic ester of cellulose, and adherent thereto at least one outer layer of a hydrotropic ester of cellulose derived from the same acid as the water-resistant ester but of lower acidyl value'than said ester.

4. A transparent window closure for an article in the use of which said closure will be exposed to conditions of temperature and humidity tending to cause'fogging by the condensation of moisture thereon, said closure comprising a layer of a water-resistant cellulose acetate, and ad herent thereto at least one outer layer of a hydrotropic cellulose acetate of lower acetyl value than the water-resistant cellulose acetate.

5. A transparent window closure for anarticle in the use of which said closure will be exposed to conditions of temperature and humidity tending to cause fogging by the condensation of moisture thereon, said closure comprising a layer of a water-resistant cellulose acetate, and adherent thereto'at least one outer layer of a hydrotropic cellulose acetate'of lower acetyl value than the water-resistant cellulose acetate, said hydrotropic cellulose acetate being soluble in aqueous acetone containing at least 50% of water but insoluble in 6. A transparent window closure for an article in the use of which said closure will be exposed to conditions of temperatureand humidity tenoing to cause fogging by the condensation of moisture thereon, said closure comprising a layer of a water-resistant organic film-forming polymer that is an ester of an organic acid, and adherent thereto at least one outer layer of a hydrotropic film-forming polymer that is an ester of the same organic acid and the same alcohol as the waterresistant polymer, said hydrotropic polymer being solublein an aqueous solution of a suitable organic liquid containing at least 50% of water, but insoluble, in water, the hydrotropic layer containing a water-soluble alcohol of high boiling point. V V

7. A transparent window closure for an article in the use of which said closure will be exposed *0 conditions of temperature and humidity tending to cause fogging by the condensation of moisture thereon, said closure comprising a layer of a water-resistant cellulose acetate, and adherent thereto at least one outer layer of a hydrotropic cellulose acetate of lower acetyl value than the water-resistant cellulose acetate, said hydrotropic cellulose acetate being soluble in aqueous acetone containing at least 50% of water but insoluble in water, and said hydrotropic layer containing glycerol.

8. A transparent Window closure for an article in the use of which said closure will be exposed to conditions of temperature and humidity tending to cause fogging by the condensation of moisture thereon, said closure comprising a layer of .acids and fatty acid esters of such acids.

-9. A transparent window closure for an article in the use of which said closure will be exposed to conditions of temperature and humidity tending to cause fogging by the condensation of moisture thereon, said closure comprising a layer of a water-resistant cellulose acetate, and adherent thereto at least one outer layer of a hydrotropic cellulose acetate of lower acetyl value than the water-resistant cellulose acetate, said hydrotropic cellulose acetate being soluble in aqueous acetone containing at least 50% of water but insoluble in water, and said hydrotropic layer containing a water-soluble methylene citric acid glycerol resin.

10. An article having a window and such that when in use said window is liable to be exposed on the inside to a moist warm atmosphere and on the outside to a colder atmosphere, said window having a transparent closure formed of composite sheet material which comprises a basic layer of a water-resistant organic film-forming polymer that is an ester of an organic acid, and adherent thereto a layer of a hydrotropic filmforming polymer that is an ester of the same organic acid and the same alcohol as the waterresistant polymer, the hydrotropic layer being on the inside of the article.

11. A respirator face-piece having an eye-piece of transparent composite sheet material which comprises a basic layer of water-resistant cellulose acetate and adherent thereto a layer of hydrotropic cellulose acetate, the hydrotropic layer being on the inside of the face-piece.

12. A respirator face-piece having an eye-piece of transparent composite sheet material which comprises a basic layer of water-resistant cellulose acetate and adherent thereto a layer oi. hydrotropic cellulose acetate which is soluble in aqueous acetone containing at least 50% of water but insoluble in water, the hydrotropic layer being on the inside of the face-piece. V

' WILLIAM HENRY MOSS. 

